The invention relates to a medical electrode comprising a foam plastic disc with an aperture to form a contact medium chamber and a foil, preferably of plastics, covering the aperture and at least a part of the foam plastic disc surrounding the aperture on one side of said disc, and a metal electrode disposed in the chamber and connected to a connector, a layer of an adhesive, preferably sensitive to pressure, being applied to the other side of the foam plastic disc.
Such electrodes are used for establishing electrical contact between the skin of humans or animals and electrical measuring equipment for measuring or detecting electrical signals or voltages produced in the skin areas in question as a result of physiological processes, such as the heart function. Plotting of curves indicative of this function is called electrocardiography, abbreviated as ECG, and electrodes of this type are therefore often called ECG electrodes.
As patients are often to be watched for long periods of time, e.g. several days, it is important that the electrodes add as little to the discomfort of the patient or carrier as possible. This is provided for to a great extent by the use of foam plastics, which is a soft and pliable material. It is also important that the paste-like contact medium, which is generally used for establishing good electrical connection between the metal electrode and the skin, can be kept intact during the entire period of operation. This means that the walls defining the contact medium chamber must be so tight as to allow no considerable diffusion of the constituent components of the contact medium.
The U.S. Patent Specification No. 3,977,392 discloses a medical electrode of the present type in which the contact medium is in direct contact with the foam plastic walls defining the aperture for receiving the medium, and though foam plastics with closed cells is used it has been found that diffusion nevertheless takes place through them, leading to deterioration of the properties of the contact medium and increased contact resistance.
The U.S. Patent Specifications No. 4,019,500 and 4,114,263 disclose medical electrodes in which diffusion of contact medium components is prevented by the use of a plastic cup which is attached to the foam plastic disc and forms the contact medium chamber. However, such plastic cups make the electrodes relatively rigid and thus add to patient discomfort.